This project is an evaluation of a novel device, the Air Barrier System (ABS), to reduce the risk of prosthesis- related surgical site infection in a multi-center clinical trial. The ABS shields surgical incisions intra-operatively by creating a field of high-purity air surrounding an incision that prevents airborne microorganisms from entering the incision. Preliminary findings in the ongoing NIH/SBIR Phase II study, after enrolling 258 patients in a single-site trial at the DeBakey Veterans Affairs Medical Center (VAMC) in Houston, indicate a positive trend for the ABS to reduce the clinical incidence of prosthesis-related infection in hip replacement, posterior spinal fusion, and prosthetic vascular graft procedures. Furthermore, preliminary data trends indicate that higher levels of airborne microorganisms in surgical theatres are correlated to an increased incidence of prosthesis-related infections and that the ABS significantly reduces the presence of these organisms during surgical procedures. Nimbic Systems has formed a consortium with researchers and surgeons at Baylor College of Medicine (VAMC and Ben Taub General hospitals) in Houston and University of Texas Medical Branch at Galveston (Texas Department of Criminal Justice Hospital). These institutions were selected specifically because the reported infection rates in the targeted surgical procedures are high; they perform a broad range of surgical services and can provide adequate enrollment volume; and patient follow-up compliance is high. Research performed will include participation by both Nimbic employees and consortium contributors. This Phase IIB research will evaluate ABS performance in a prospective, randomized, blinded multi-center trial expanded to 816 surgical cases. The surgical procedures studied will include total hip arthroplasty, trauma- related acetabula reconstruction, posterior instrumented spine fusion, and prosthetic vascular graft procedures. Patients will be enrolled during the first two years of the study, and CDC guidelines require a one year follow- up period to monitor patients for potential prosthesis-related infections. The project's key aims are to: (1) compare the incidence of implant-related infections between the control and ABS groups, (2) determine whether increased levels of airborne microorganisms in surgical theatres are correlated to an increase in the incidence of surgical site infections, (3) determine if a risk-assessment model can be constructed to predict the incidence of infection based on airborne CFU levels, (4) evaluate user satisfaction with the ABS device and develop device improvements.